This invention relates to a medical diagnostic ultrasound system and method for automated triggering, such as for use in perfusion imaging or studies. In particular, automated triggering is used for determining perfusion using contrast agents.
Various methods of imaging contrast agents have been proposed for measuring perfusion or perfusion-related parameters. For example, a method is described by Dr. Wei in "Quantification of Myocardial Blood Flow with Ultrasound-Induced Destruction of Microbubbles Administered as a Constant Venous Infusion", Circulation, volume 97, pp. 473-487, 1998. Using an ECG signal, images of microbubbles are generated by an ultrasound system at fixed trigger intervals. As each image is generated after a trigger interval, the microbubbles are destroyed. The amount of contrast agent that reflows into a region of interest during the trigger interval as represented on the subsequent image is measured. A fixed trigger interval is then manually changed and the measurement is repeated. Based on these measurements, a re-flow curve showing the amount of contrast agent flowing into a region as a function of the trigger interval is plotted. Due to the manual change of the trigger interval, an unnecessarily long amount of time is required to acquire the images and measure the amount of contrast agent re-flow.
Other triggering schemes for imaging contrast agents are known, such as shown in U.S. Pat. No. 5,833,613. An ultrasonic transmission is triggered off of an ECG signal to destroy contrast agent. Within the same heartbeat, an image is generated at a certain time after transmission of the destructive ultrasonic energy. The time between the transmission for destruction and transmissions for imaging is varied within the heartbeat. Other triggering schemes are shown for example in U.S. Pat. No. 5,686,310.
To assist a clinician during trigger imaging of contrast agent, images generated using low-power transmission may be interleaved with the trigger or destructive transmissions. The images allow the user to maintain the transducer in the correct position relative to the region of interest with reduced destruction of the contrast agents. Such imaging is taught, for example, in U.S. Pat. No. 6,110,120 (U.S. application Ser. No. 08/838,919), filed Apr. 11, 1997.